Surveillance and monitoring systems for intercepting communications between transmitters in cellular telephone systems are used by law enforcement and operational support system providers to monitor the traffic and sometimes the content of the communications on such transmitters, referred to as user equipment (UE) in the following discussion.
Monitoring systems for communications in earlier cellular systems tapped a point in the data flow that is no longer available in 4G networks. In addition, the data that is available is in the form of base-band carrier data that encodes the entire set of transmissions between the cellular transmitter and all of the UE in a cell. The cost of a monitoring system that decodes all of the data is a significant barrier to the implementation of such systems. In addition, the monitoring station capabilities would depend on the location of the monitor in the particular cell, since not all UE may be visible at a particular location within the cell.